A 60-year-old woman presented with a 10-cm hepatic cyst that was anechoic on ultrasound and a serum carbohydrate antigen (CA) 19-9 concentration of 50.7 U/ml. Ultrasonography six months later revealed that the diameter of the cyst had increased to 12 cm, accompanied by a small papillary region arising from the cyst wall and intracystic echoes representing debris.The serum CA19-9 level had increased to 89.2 U/ml. At this time, abdominal contrast-enhanced computed tomography, esophagogastroduodenoscopy, and colonoscopy did not reveal any intracystic tumors. Intracystic hemorrhage was diagnosed based on cyst fluid cytology, but the patient had no abdominal pain or anemia. Ultrasonography at nine months showed growth of the papillary region and the serum CA19-9 level was 385.7 U/ml. Serum CA19-9 peaked at 1014.0 U/ml at 12 months, but ultrasonography showed no remarkable changes